Antiestrogens As Antitumor Drugs

Antiestrogens can be defined as compounds that prevent the stimulation of transcription by the ER. Two main types of antiestrogens are known:

a. Nonsteroidal antiestrogens, which interfere with the transcription process by binding to the hormone recognition site in the ER and preventing the induction of the conformational change necessary for recognition of the coactivators. Since ERs of different target tissues vary in chemical structure, these compounds may show mixed biological responses because they can behave as antagonists in one estrogen target tissue and as agonists in another. In spite of not being completely selective, compounds of this group are often designed as selective estrogen receptor modulators (SERMs).

b. Pure antiestrogens are analogs of the natural hormones that bear long, flexible side chains at C-7. These compounds bind to the ER and prevent receptor binding to DNA, probably because the side chains bind to the receptor outside the steroid-binding region.

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